The present invention relates to power tools.
Publication U.S. Pat. No. 6,800,045 B1 makes known a power tool, in the form of a drill, the gearbox of which is coupled to the drive motor and is connected to an auxiliary gear device. The auxiliary gear device automatically lowers the gear ratio during operation in accordance with the resistance to rotation presented. This means, for instance, that the rotational speed of the gearbox is reduced during drilling operation if the hardness of the material to be drilled increases. This is made possible via the known auxiliary gear device without the need to stop the drive.
Furthermore, it is made known in JP 7308813A to provide a shifting device on a column drill, the shifting device making it possible to change gears rapidly during operation. Further details, in particular those regarding the control of rotational speed during gear shifting, are not provided in the document.
From U.S. Pat. No. 6,978,846 it is known, with regard for a torque-controlled impact driver, to adapt the rotational speed of the drive to the torque required to drive a screw, and to the screw-driving status. In the case of the known impact driver, it is not possible to shift gears while driving a screw.
From U.S. Pat. No. 5,754,019 it is known to control the electric motor of a power tool such that it is automatically switched to another operating state once a limiting torque is reached. In this other operating state, the tool switches to indexed operation, e.g., when a screw is being driven, and the screw is driven completely into place. The motor speeds and/or time intervals of motor operation that occur during the other operating state may be adapted as needed.
From U.S. Pat. No. 6,398,678 B1 it is known to change the rotational speed of the drive motor of a power tool without having to stop the drive motor. This is realized via manual input to a wheel that changes the position of a transmission belt located between bevel gears.